3-Methyl-thiofentanyl was sold briefly on the black market in the early 1980s, before the introduction of the Federal Analog Act which for the first time attempted to control entire families of drugs based on their structural similarity rather than scheduling each drug individually as they appeared. [1]

3-Methyl-thiofentanyl has similar effects to fentanyl. Side effects of fentanyl analogues are similar to those of fentanyl itself, which include itching, nausea and potentially serious respiratory depression which can be life-threatening.